Turbocharging units are a commonly used way to increase the power of an engine, both With conventional internal combustion engines, and Diesel engines. Turbochargers are comprised of a turbine, and a compressor. The turbine receives exhaust gas from the exhaust manifold of the engine, and the turbine wheel located inside the turbine rotates, powering a compressor wheel inside the compressor. The compressor forces high-pressure air into the intake manifold of the engine, increasing power output.
Due to increased environmental concerns, an emphasis has been placed on reducing the amount of exhaust gas emissions of both internal combustion engines and diesel engines. One method that has been used to reduce exhaust gas emissions has been to reintroduce the exhaust gas into the intake manifold of the engine, reducing the amount of exhaust gas released into the atmosphere. This is commonly achieved through the use of an EGR valve.
Current and future emission requirements for diesel engines in Europe, the U.S., and most foreign markets require engine concepts capable of delivering high EGR-rates at very low vehicle loads/speeds. One way of providing these EGR-rates is by using low pressure EGR. However, exhaust gas can contain a high amount of water vapor, dependent on the humidity of the air and the fuel quantity burned in the combustion chamber of the engine. The path the exhaust gas flows through, also called the EGR path, is comprised of the turbocharger, a particulate filter, an exhaust pipe, an EGR path having an EGR valve, a low-pressure EGR path having a low pressure EGR valve, and a low pressure EGR cooler. While the water vapor passes through the EGR path, at certain driving conditions such as cold ambient temperature, or low engine loads and therefore low exhaust temperatures after a cold start, the water vapor cools down below its dew point temperature and droplets are formed. These droplets of different aerodynamic radii pass through the EGR path, the low-pressure EGR path, the low pressure EGR cooler, and into the intake pipe in front of the rotating compressor wheel, also called the mixing area.
One major problem caused by the droplets coming into contact with the compressor wheel is that these droplets that are formed can lead to massive droplet erosion on the compressor wheel. One way to keep droplets from hitting the compressor wheel in a critical area is to have the droplets permanently removed from the flow of exhaust gas going into the compressor wheel under all driving conditions. It is very difficult to permanently remove the condensate from the intake side because of the negative pressure drop to atmosphere (pumping would be necessary). Also humidity in the intake air is a positively influencing parameter for in-cylinder NOx reduction.
Another way to keep droplets from hitting the compressor wheel area is to temporarily separate the condensate from the gas flow, and then re-introduce the liquid condensate into the exhaust gas in an area to avoid corrosion of the blades on the compressor wheel. This is difficult because dispersion of liquid condensate can cause damage to the compressor wheel blades.
Accordingly, an object of the present invention is to bring the water vapor or condensate from the exhaust gas of the engine into close contact with the compressor wheel in an area of low blade speed to prevent erosion of the compressor wheel.